(1) Field of the Invention
The present invention relates to a track access control system including coarse and fine (speed and position) control for positioning a head (for example, magnetic or optical head) for writing and/or reading data, above a target track on a surface of a rotating disc (for example, magnetic or magneto-optical disc) on which digital data is memorized, in a rotating disc device (for example, magnetic or magneto-optical disc device).
(2) Description of the Related Art
The track access control system in the rotating disc device is a servo control system wherein information on a real speed of the head and a real driving current of a moving mechanism (for example, a voice coil motor) of the head, are fedback to a controller of the track access control system, and the moving mechanism is controlled based on a target speed of the head and the above fedback information, in the coarse (speed) control operation; and information on a real position of the head is fedback to the controller to control the moving mechanism to position the head above the target track, in the fine (position) control operation. In the track access control system, there are a plurality of parameters which are to be adjusted to optimum values, in a factory before packing for shipment.
Until now, the above track access control system has been automatically adjusted to the optimum setting condition by trial and error. That is, the optimum setting condition is obtained by giving various values for the above parameters, and examining the performance of the track access control system for the various values. The operation of the automatic adjustment is described in detail in the above copending application Ser. No. 460, 657.
However, during a coarse (speed) control operation which is carried out in the above automatic adjustment operation, or other operations for examining the track access control system preceding the adjustment operation, the movement of the head often stops unintentionally due to the track access control system being out of the optimum condition. When the head stops at an intended position, the above automatic adjustment operation, or the above other operation for examining the track access control system cannot be further continued automatically, so that such a situation is recognized as an error, and causes problems and delay in the above operations. Further, a similar unintentional stop may occur during use of the rotating disc device due to a deviation from the optimum condition by aging, or an influence of an external disturbance.
In addition, a return-to-zero operation is often required to be carried out during the above automatic adjustment operation, or other operation of the track access control system before and after the adjustment operation. The return-to-zero operation is an operation to position the head above the zero track, and is carried out to initialize the position of the head. A very small target speed is used in the return-to-zero operation because, generally, it is unknown how far from the zero track position the starting position of the head is. The present applicant found that, when the track access control system is out of the optimum condition before the adjustment or due to aging or an external disturbance, the real speed of the head is likely to be much smaller than a target speed for the coarse (speed) control operation in the return-to-zero operation, thus causing a great deal of delay in the return-to-zero operation. Therefore, the efficiency of the above operation is greatly reduced by the above delay.